Resonant conversion system and control method

Abstract

This application provides a resonant conversion system, including a controller and a resonant conversion circuit. The resonant conversion circuit includes a high frequency chopper circuit, a resonant cavity, a transformer, and a rectification filter network, and the high frequency chopper circuit includes switches S1 and S2. The controller is configured to: detect a bridge arm midpoint voltage VSW, and determine based on the VSW a current threshold signal used to indicate a current threshold; detect a resonant current on a primary side of the transformer, and compare the resonant current with the current threshold signal to control on/off of the switch S1 or S2 based on the second electrical signal, so that the system operates in an inductive mode to ensure zero voltage switching of the switch, while operating in a state close to a capacitive mode to maximize the use of a gain region.

The invention claimed is: 
     
       1. A resonant conversion system, comprising:
 a controller; and 
 a resonant conversion circuit comprising a high frequency chopper circuit, a resonant cavity, a transformer, and a rectification filter network, wherein the high frequency chopper circuit comprises switches S 1  and S 2 , the controller is configured to control on/off of the switches S 1  and S 2  to convert a direct current voltage input to the high frequency chopper circuit into a high frequency square wave, the resonant cavity and the transformer are configured to receive the high frequency square wave and couple electrical energy from a primary side of the transformer to a secondary side, and the rectification filter network is configured to convert an alternating current voltage coupled to the secondary side of the transformer into a direct current voltage; and 
 the controller is further configured to: 
 detect a bridge arm midpoint voltage V SW , and determine a first electrical signal based on the bridge arm midpoint voltage V SW , wherein the bridge arm midpoint voltage V SW  is a voltage of a bridge arm midpoint connected to the switches S 1  and S 2 , and the first electrical signal has an association relationship with a slope of the bridge arm midpoint voltage V SW ; 
 determine a current threshold signal based on the first electrical signal, wherein the current threshold signal is used to indicate a current threshold; 
 detect a resonant current on the primary side of the transformer, and compare the resonant current with the current threshold signal to determine a second electrical signal, wherein the second electrical signal is used to indicate a comparison result; and 
 control on/off of the switch S 1  or S 2  based on the second electrical signal, so that the system operates in an inductive mode. 
 
     
     
       2. The system according to  claim 1 , wherein the first electrical signal comprises a first pulse signal slp 1  and a second pulse signal slp 2 , and the controller is specifically configured to:
 detect the bridge arm midpoint voltage V SW , and determine a slope signal V SLP  based on the bridge arm midpoint voltage V SW , wherein the slope signal V SLP  indicates the slope of the bridge arm midpoint voltage V SW ; 
 determine the first pulse signal slp 1  based on the slope signal V SLP  and a first slope threshold V TH1 , wherein a pulse length of the first pulse signal slp 1  is used to indicate duration tslp 1  in which the slope signal V SLP  is greater than the first slope threshold V TH1 ; and 
 determine the second pulse signal slp 2  based on the slope signal V SLP  and a second slope threshold V TH2 , wherein a pulse length of the second pulse signal slp 2  is used to indicate duration tslp 2  in which the slope signal V SLP  is less than the second slope threshold V TH2 , and the second slope threshold V TH2  is less than the first slope threshold V TH1 . 
 
     
     
       3. The system according to  claim 2 , wherein the current threshold signal comprises a first current threshold signal used to indicate a first current threshold ith 1  and a second current threshold signal used to indicate a second current threshold ith 2 , and the controller is further configured to:
 determine the first current threshold signal and the second current threshold signal based on the first pulse signal slp 1  and the second pulse signal slp 2 , wherein the controller is specifically configured to: 
 determine a first initial current threshold and a second initial current threshold, wherein the first initial current threshold is a positive value, and the second initial current threshold is a negative value; 
 compare the duration tslp 1  indicated by the pulse length of the first pulse signal slp 1  with a first time threshold Tth 1 , and when the duration tslp 1  indicated by the pulse length of the first pulse signal slp 1  is greater than the first time threshold Tth 1 , decrease the first initial current threshold to obtain the first current threshold ith 1 , or when the duration tslp 1  indicated by the pulse length of the first pulse signal slp 1  is less than the first time threshold Tth 1 , increase the first initial current threshold to obtain the first current threshold ith 1 ; and 
 compare the duration tslp 2  indicated by the pulse length of the second pulse signal slp 2  with a second time threshold Tth 2 , and when the duration tslp 2  indicated by the pulse length of the second pulse signal slp 2  is greater than the second time threshold Tth 2 , increase the second initial current threshold to obtain the second current threshold ith 2 , or when the duration tslp 2  indicated by the pulse length of the second pulse signal slp 2  is less than the second time threshold Tth 2 , decrease the second initial current threshold to obtain the second current threshold ith 2 . 
 
     
     
       4. The system according to  claim 1 , wherein the first electrical signal is a slope signal V SLP , the slope signal V SLP  indicates the slope of the bridge arm midpoint voltage V SW , and the controller is specifically configured to:
 detect the bridge arm midpoint voltage V SW , and determine the slope signal V SLP  based on the bridge arm midpoint voltage V SW . 
 
     
     
       5. The system according to  claim 4 , wherein the current threshold signal comprises a first current threshold signal used to indicate a first current threshold ith 1  and a second current threshold signal used to indicate a second current threshold ith 2 , and the controller is further configured to:
 determine the first current threshold signal and the second current threshold signal based on the slope signal V SLP , wherein the controller is specifically configured to: 
 determine a first initial current threshold and a second initial current threshold, wherein the first initial current threshold is a positive value, and the second initial current threshold is a negative value; 
 compare the slope signal V SLP  with a third slope threshold V TH3 , and when the slope signal V SLP  is greater than the third slope threshold V TH3 , decrease the first initial current threshold to obtain the first current threshold ith 1 , or when the slope signal V SLP  is less than the third slope threshold V TH3 , increase the first initial current threshold to obtain the first current threshold ith 1 ; and 
 compare the slope signal V SLP  with a fourth slope threshold V TH4 , and when the slope signal V SLP  is greater than the fourth slope threshold V TH4 , increase the second initial current threshold to obtain the second current threshold ith 2 , or when the slope signal V SLP  is less than the fourth slope threshold V TH4 , decrease the second initial current threshold to obtain the second current threshold ith 2 , wherein the fourth slope threshold V TH4  is less than the third slope threshold V TH3 . 
 
     
     
       6. The system according to  claim 1 , wherein the second electrical signal comprises a first switching signal ic 1  and a second switching signal ic 2 , and the controller is further configured to:
 detect the resonant current icr on the primary side of the transformer; and 
 determine the first switching signal ic 1  and the second switching signal ic 2  based on the resonant current icr and the current threshold signal, wherein the current threshold signal comprises the first current threshold signal used to indicate the first current threshold ith 1  and the second current threshold signal used to indicate the second current threshold ith 2 , and the controller is specifically configured to: 
 compare the resonant current icr with the first current threshold ith 1 , and when the resonant current icr is greater than the first current threshold ith 1 , determine that the first switching signal ic 1  is used to indicate to turn on the switch S 1 , or when the resonant current icr is less than the first current threshold ith 1 , determine that the first switching signal ic 1  is used to indicate to turn off the switch S 1 ; and 
 compare the resonant current icr with the second current threshold ith 2 , and when the resonant current icr is greater than the second current threshold ith 2 , determine that the second switching signal ic 2  is used to indicate to turn off the switch S 2 , or when the resonant current icr is less than the second current threshold ith 2 , determine that the second switching signal ic 2  is used to indicate to turn on the switch S 2 . 
 
     
     
       7. The system according to  claim 6 , wherein the controller is specifically configured to:
 determine a first control signal DR 1  based on the first switching signal ic 1 , wherein the first control signal DRV 1  is used to control on/off of the switch S 1 ; and 
 determine a second control signal DRV 2  based on the second switching signal ic 2 , wherein the second control signal DRV 2  is used to control on/off of the switch S 2 . 
 
     
     
       8. The system according to  claim 1 , wherein the controller comprises:
 a slope detection circuit, a threshold control circuit, a current comparison circuit, and a switching control circuit. 
 
     
     
       9. The system according to  claim 8 , wherein the slope detection circuit comprises:
 a detection capacitor Csw and a detection resistor Rsw, wherein 
 a first end of the detection capacitor Csw is configured to receive the bridge arm midpoint voltage Vsw, a second end of the detection capacitor Csw is connected to a first end of the detection resistor Rsw, a second end of the detection resistor Rsw is grounded, and the first end of the detection resistor Rsw is configured to output the slope signal V SLP . 
 
     
     
       10. The system according to  claim 8 , wherein
 the slope detection circuit further comprises a first comparator CMP 1 , a second comparator CMP 2 , and a first NOT gate INV 1 , wherein 
 a first input end and a second input end of the first comparator CMP 1  are configured to receive the slope signal V SLP  and a signal of the first slope threshold V TH1  respectively, and an output end of the first comparator CMP 1  is configured to output the first pulse signal slp 1 ; and 
 a first input end and a second input end of the second comparator CMP 2  are configured to receive the slope signal V SLP  and a signal of the second slope threshold V TH2  respectively, an output end of the second comparator CMP 2  is connected to an input end of the first NOT gate INV 1 , and an output end of the first NOT gate INV 1  is configured to output the second pulse signal slp 2 . 
 
     
     
       11. The system according to  claim 8 , wherein the current comparison circuit comprises:
 a third comparator CMP 3 , a fourth comparator CMP 4 , and a second NOT gate INV 2 , wherein 
 a first input end and a second input end of the third comparator CMP 3  are configured to receive the resonant current icr and the first current threshold ith 1  respectively, and an output end of the third comparator CMP 3  is configured to output the first switching signal ic 1 ; and 
 a first input end and a second input end of the fourth comparator CMP 4  are configured to receive the resonant current icr and the second current threshold ith 2  respectively, an output end of the fourth comparator CMP 4  is connected to an input end of the second NOT gate INV 2 , and an output end of the second NOT gate INV 2  is configured to output the second switching signal ic 2 . 
 
     
     
       12. A method for controlling a resonant conversion system, wherein the resonant conversion system comprises:
 a controller; and 
 a resonant conversion circuit comprising a high frequency chopper circuit, a resonant cavity, a transformer, and a rectification filter network, wherein the high frequency chopper circuit comprises switches S 1  and S 2 , the controller is configured to control on/off of the switches S 1  and S 2  to convert a direct current voltage input to the high frequency chopper circuit into a high frequency square wave, the resonant cavity and the transformer are configured to receive the high frequency square wave and couple electrical energy from a primary side of the transformer to a secondary side, and the rectification filter network is configured to convert an alternating current voltage coupled to the secondary side of the transformer into a direct current voltage; and 
 the method comprises: 
 detecting, by the controller, a bridge arm midpoint voltage V SW , and determining a first electrical signal based on the bridge arm midpoint voltage V SW , wherein the bridge arm midpoint voltage V SW  is a voltage of a bridge arm midpoint connected to the switches S 1  and S 2 , and the first electrical signal has an association relationship with a slope of the bridge arm midpoint voltage V SW ; 
 determining, by the controller, a current threshold signal based on the first electrical signal, wherein the current threshold signal is used to indicate a current threshold; 
 detecting, by the controller, a resonant current on the primary side of the transformer, and comparing the resonant current with the current threshold signal to determine a second electrical signal, wherein the second electrical signal is used to indicate a comparison result; and 
 controlling, by the controller, on/off of the switch S 1  or S 2  based on the second electrical signal, so that the system operates in an inductive mode. 
 
     
     
       13. The method according to  claim 12 , wherein the first electrical signal comprises a first pulse signal slp 1  and a second pulse signal slp 2 ; and
 the detecting, by the controller, a bridge arm midpoint voltage V SW , and determining a first electrical signal based on the bridge arm midpoint voltage V SW  comprises: 
 detecting, by the controller, the bridge arm midpoint voltage V SW , and determining a slope signal V SLP  based on the bridge arm midpoint voltage Vsw, wherein the slope signal V SLP  indicates the slope of the bridge arm midpoint voltage V SW ; 
 determining, by the controller, the first pulse signal slp 1  based on the slope signal V SLP  and a first slope threshold V TH1 , wherein a pulse length of the first pulse signal slp 1  is used to indicate duration tslp 1  in which the slope signal V SLP  is greater than the first slope threshold V TH1 ; and 
 determining, by the controller, the second pulse signal slp 2  based on the slope signal V SLP  and a second slope threshold V TH2 , wherein a pulse length of the second pulse signal slp 2  is used to indicate duration tslp 2  in which the slope signal V SLP  is less than the second slope threshold V TH2 , and the second slope threshold V TH2  is less than the first slope threshold V TH1 .